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Spring 07 Exam 5 Key - CHEMISTRY 225 TEST#5 JUNE.15 2007...

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Unformatted text preview: CHEMISTRY 225 TEST #5 JUNE .15, 2007 1. (16) A 2. (21) NAME "‘ m 9m.) (5 v 3. (11) 4. __ (19) 5. (03) TOTAL (75) GOOD LUCK! . (16 Points) ORGANIC REACTIONS. Cornplete FOUR of the following reactions by providing structures for the reactant, product, or reagent as required. If no reaction is expected under the reaction conditions, write “NR.” and explain briefly why the reaction fails. If you complete all five reactions, pZease indicate clearly whichfour you wish to have graded. All reactions carry equal point value. G) H'WC—O + CH3CHZBI' t? C Et/ ““0 ——~913L—» I (+ NaCI) acetone Ph 91*) 2 (Ph = phenyl) Org. Left. 2007, 9, 1951 (CH3)3N + H20 an“- 2. (21 Points) REACTION MECHANISMS. a. ( I 6) In the Chemistry 227 lab alcohols are converted to alkyl halides by treatment with sodium bromide in sulfuric acid. The reaction proceeds by way of the conjugate acid of the alcohol. The second step is an 3N2 reaction. The process is illustrated below for l-butanol. e i —»B‘ in»; Cite/cage, i o (2) Write a structure for the cationic intermediate in this reaction sequence. NaBr —+ - . 0 H CH3CHZCHQCH20H H2804 %% 04- CAL B 2 o (1) Add mechanistic arrows to Show the course of the second step. 0 (2) Complete the reaction sequence with a structure for the product. I (1) Identify the leaving group in the second step. H5 U b. ( f 1 1) Consider the ether synthesis below: OCH3 o (1) Write the rate law for the formation of the ether product. Quit 2 JE, [C7 L] t S 9‘3] I (5) Complete the “minimechani 5111” with structures for the two intermediates. Add mechanistic arrows to show the “flow” of an electron pair. o (2) Write the structure of an additional product that would be formed under these reaction conditions. 0 (3) The second step of the SN] reaction above is highly exothermic. Use this information and the Hammond Postulate to deduce certain properties of the transition state for this step. Underline the correct description. In the transition state: -The new C-O bond is _ just starting to form almost fully formed - The central carbon atom is nearly electrically neutral _ bears almost a full positive charge - The geometry at the central carbon atom is very close to trigonal planar very nearly tetrahedral c. ( f 4) Bromocyelohexane reacts with cyanide ion by an 3N2 mechanism. Sketch a picture of the transition state for the substitution reaction below. NOTE: both reactant and product are shown in their more stable chair confornéations. N L. ‘ \ ‘ 1»! Br A ‘ fl: p\ ‘ B the transition state 4 3. (11 Points) KINETICS AND THERMODYNAMICS - '5; a. ( r’ 7) Consider the hypothetical reaction represented by the reaction coordinate diagram to the .4: right. “1 k2 \_/\ B A B ““ C K1 k_2 A L...—..._._.. C o (i) Label all transition states with double daggers (t) reaction coordinate I (1) Identify the rate-determining step in the forward direction @ “-9 C o (3) Determine the relative magnitudes of the rate constants _,£,_ ( > J ‘ >/€ > .xg - z o (1) Which species will be present in highest concentration if the reaction reaches equilibrium? (2 o (1) Identify the conversion of B -—> A as ' 9 Endergonic Equigonic @ b. ( f 4) Use the covalent bond energies to the right to Bond DH0 (koalimole) determine AH for the reaction below. To insure maximum credit for your answer, Show your work clearly. 0—8 83 C“) {3—H 99 C + HwOH ——+ H C—C—CH H30” \CH3 3 I 3 86 4. (19 Points) SUBSTITUTION REACTIONS a. ( / 5) Intramolecular substitution reactions are particulariy useful because they form rings. Complete the following cyclization reaction sequence with a structure for the intermediate and the cyclized product. Add a “squiggly” line to show the bond formed in the product. 5 b. ( f 6) The final step in the synthesis of (+)-muscarine iodide (Test #4) was a substitution reaction using trimethylamine [Tetrahedron Left. 2007, 48, 29?1]. 0 (3) Complete the equation below with a structure for the electrophilei - (3) Suggest an alternate combination of reactants for the synthesis of (+)-muscarine iodide in which a dfflerenr C-N bond is formed in a substitution reaction. Ho, .1 9H3 + N(CH3)3 ——» DVNQCHS ie H3O O I CH3 (+)—muscarine iodide (alternate route) c. ( I 5) Consider the substitution reaction sequence below [Tetrahedron Lett. 2007, 48, 3705]: OH 030ch3 9 I33 ROJfi/{CHM _CH35020'_., ROJYsz)” _..Ns RON/At (CH2)11 OCHgPh I OCHzPh OCHzPh {a sutfonate ester) 0 (3) What is the purpose of converting the hydroxyl group to a sulfonate ester in the first step? Whyisflfisneceismy'? chwaq‘efi “r, W Lwlwfiowefiifi gs. Lt. 1,4» dee- +0=eouue~ Ti“ -- 6TH we“ +0 a 09 (7i iedi-iwo 31/0417 (its: wefiawe t-giZLDa-AZLL ”unflbijW/L‘d 9LT: Jrfi- ED \r-e arc-ea H) La QCILAC-E. 0 H ~19 Q‘i—{Vv' I]; Le, [’60. «.«IJU 31/0 L4?) Aiwipoik owe xix—vie. eigasiwai} ‘1“ 9N8 VC$CJ_9M¢_ - (2) By what mechanistic type is the second step occurring? How do you know? QFZ » 713-9 79 6L (‘HLQLcl-Ml'tflm reac‘imaa—t ULQJ— Kit, odCQL~v\-. w.kj/[A ‘(mvf-“IIOU. Q47 “11¢.Ctavimm Leas-f3 TL; ieau-U jv’DM-f- 6 d. ( f 3) An analogous two-step reaction sequence was used by chemists in India in the course of a synthesis of the antibiotic (+)-negamycin [Tetrahedron Lett. 2007, 48, 3705]. Complete the reaction with a structure for the product. OP oH ? : 1. CH380201 0‘? N9 \\ .. 2. NaN3 A (P = protecting group, doesn‘t participate in reaction) compound A e. ( i’ 4) BONUS QUESTION! The synthesis of (+)—negamycin included further transformations of compound A above. Deduce the structure of the product when compound A is treated with two additional nucleophilic reagents. HINT: the product of the first reaction becomes the reactant for the second. N | NaN CompoundA —~g—a- —3» 5. (08 Points) MULTIPLE CHOICE, ETC. 0 Circle the structure of the Lewis acid; underline the structure of the Lewis base. (s CH4 CH30H CHgBl' (C H3)3C I Circle the species that is both a strong nucleophile and a good leaving group; underline the species that is both a strong base and a strong nucleophile. e e ' ' CHgCHZOH CH3C H20 CN 0 Circle the most reactive compound in the SN] reaction; underline the'rnost reactive compound in the 8N2 reaction. C H2 B r - Cir. common solvent for the SN] reaction; underline a polar aprotic solvent. CH3CH20 CH3CHZOCHZCH3 CH30H20H20H2CH20H3 DMF ...
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